<?php
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  AES implementation in PHP (c) Chris Veness 2005-2009. Right of free use is granted for all    */
/*    commercial or non-commercial use under LGPL licence. No warranty of any form is offered.    */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */


/**
 * AES Cipher function: encrypt 'input' with Rijndael algorithm
 *
 * @param input message as byte-array (16 bytes)
 * @param w     key schedule as 2D byte-array (Nr+1 x Nb bytes) - 
 *              generated from the cipher key by KeyExpansion()
 * @return      ciphertext as byte-array (16 bytes)
 */
function Cipher($input, $w) {    // main Cipher function [§5.1]
  $Nb = 4;                 // block size (in words): no of columns in state (fixed at 4 for AES)
  $Nr = count($w)/$Nb - 1; // no of rounds: 10/12/14 for 128/192/256-bit keys

  $state = array();  // initialise 4xNb byte-array 'state' with input [§3.4]
  for ($i=0; $i<4*$Nb; $i++) $state[$i%4][floor($i/4)] = $input[$i];

  $state = AddRoundKey($state, $w, 0, $Nb);

  for ($round=1; $round<$Nr; $round++) {  // apply Nr rounds
    $state = SubBytes($state, $Nb);
    $state = ShiftRows($state, $Nb);
    $state = MixColumns($state, $Nb);
    $state = AddRoundKey($state, $w, $round, $Nb);
  }

  $state = SubBytes($state, $Nb);
  $state = ShiftRows($state, $Nb);
  $state = AddRoundKey($state, $w, $Nr, $Nb);

  $output = array(4*$Nb);  // convert state to 1-d array before returning [§3.4]
  for ($i=0; $i<4*$Nb; $i++) $output[$i] = $state[$i%4][floor($i/4)];
  return $output;
}


function AddRoundKey($state, $w, $rnd, $Nb) {  // xor Round Key into state S [§5.1.4]
  for ($r=0; $r<4; $r++) {
    for ($c=0; $c<$Nb; $c++) $state[$r][$c] ^= $w[$rnd*4+$c][$r];
  }
  return $state;
}

function SubBytes($s, $Nb) {    // apply SBox to state S [§5.1.1]
  global $Sbox;  // PHP needs explicit declaration to access global variables!
  for ($r=0; $r<4; $r++) {
    for ($c=0; $c<$Nb; $c++) $s[$r][$c] = $Sbox[$s[$r][$c]];
  }
  return $s;
}

function ShiftRows($s, $Nb) {    // shift row r of state S left by r bytes [§5.1.2]
  $t = array(4);
  for ($r=1; $r<4; $r++) {
    for ($c=0; $c<4; $c++) $t[$c] = $s[$r][($c+$r)%$Nb];  // shift into temp copy
    for ($c=0; $c<4; $c++) $s[$r][$c] = $t[$c];         // and copy back
  }          // note that this will work for Nb=4,5,6, but not 7,8 (always 4 for AES):
  return $s;  // see fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf 
}

function MixColumns($s, $Nb) {   // combine bytes of each col of state S [§5.1.3]
  for ($c=0; $c<4; $c++) {
    $a = array(4);  // 'a' is a copy of the current column from 's'
    $b = array(4);  // 'b' is a•{02} in GF(2^8)
    for ($i=0; $i<4; $i++) {
      $a[$i] = $s[$i][$c];
      $b[$i] = $s[$i][$c]&0x80 ? $s[$i][$c]<<1 ^ 0x011b : $s[$i][$c]<<1;
    }
    // a[n] ^ b[n] is a•{03} in GF(2^8)
    $s[0][$c] = $b[0] ^ $a[1] ^ $b[1] ^ $a[2] ^ $a[3]; // 2*a0 + 3*a1 + a2 + a3
    $s[1][$c] = $a[0] ^ $b[1] ^ $a[2] ^ $b[2] ^ $a[3]; // a0 * 2*a1 + 3*a2 + a3
    $s[2][$c] = $a[0] ^ $a[1] ^ $b[2] ^ $a[3] ^ $b[3]; // a0 + a1 + 2*a2 + 3*a3
    $s[3][$c] = $a[0] ^ $b[0] ^ $a[1] ^ $a[2] ^ $b[3]; // 3*a0 + a1 + a2 + 2*a3
  }
  return $s;
}

/**
 * Key expansion for Rijndael Cipher(): performs key expansion on cipher key
 * to generate a key schedule
 *
 * @param key cipher key byte-array (16 bytes)
 * @return    key schedule as 2D byte-array (Nr+1 x Nb bytes)
 */
function KeyExpansion($key) {  // generate Key Schedule from Cipher Key [§5.2]
  global $Rcon;  // PHP needs explicit declaration to access global variables!
  $Nb = 4;              // block size (in words): no of columns in state (fixed at 4 for AES)
  $Nk = count($key)/4;  // key length (in words): 4/6/8 for 128/192/256-bit keys
  $Nr = $Nk + 6;        // no of rounds: 10/12/14 for 128/192/256-bit keys

  $w = array();
  $temp = array();

  for ($i=0; $i<$Nk; $i++) {
    $r = array($key[4*$i], $key[4*$i+1], $key[4*$i+2], $key[4*$i+3]);
    $w[$i] = $r;
  }

  for ($i=$Nk; $i<($Nb*($Nr+1)); $i++) {
    $w[$i] = array();
    for ($t=0; $t<4; $t++) $temp[$t] = $w[$i-1][$t];
    if ($i % $Nk == 0) {
      $temp = SubWord(RotWord($temp));
      for ($t=0; $t<4; $t++) $temp[$t] ^= $Rcon[$i/$Nk][$t];
    } else if ($Nk > 6 && $i%$Nk == 4) {
      $temp = SubWord($temp);
    }
    for ($t=0; $t<4; $t++) $w[$i][$t] = $w[$i-$Nk][$t] ^ $temp[$t];
  }
  return $w;
}

function SubWord($w) {    // apply SBox to 4-byte word w
  global $Sbox;  // PHP needs explicit declaration to access global variables!
  for ($i=0; $i<4; $i++) $w[$i] = $Sbox[$w[$i]];
  return $w;
}

function RotWord($w) {    // rotate 4-byte word w left by one byte
  $tmp = $w[0];
  for ($i=0; $i<3; $i++) $w[$i] = $w[$i+1];
  $w[3] = $tmp;
  return $w;
}

// Sbox is pre-computed multiplicative inverse in GF(2^8) used in SubBytes and KeyExpansion [§5.1.1]
$Sbox =  array(0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
               0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
               0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
               0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
               0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
               0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
               0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
               0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
               0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
               0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
               0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
               0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
               0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
               0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
               0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
               0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16);

// Rcon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]
$Rcon = array( array(0x00, 0x00, 0x00, 0x00),
               array(0x01, 0x00, 0x00, 0x00),
               array(0x02, 0x00, 0x00, 0x00),
               array(0x04, 0x00, 0x00, 0x00),
               array(0x08, 0x00, 0x00, 0x00),
               array(0x10, 0x00, 0x00, 0x00),
               array(0x20, 0x00, 0x00, 0x00),
               array(0x40, 0x00, 0x00, 0x00),
               array(0x80, 0x00, 0x00, 0x00),
               array(0x1b, 0x00, 0x00, 0x00),
               array(0x36, 0x00, 0x00, 0x00) ); 


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/** 
 * Encrypt a text using AES encryption in Counter mode of operation
 *  - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
 *
 * Unicode multi-byte character safe
 *
 * @param plaintext source text to be encrypted
 * @param password  the password to use to generate a key
 * @param nBits     number of bits to be used in the key (128, 192, or 256)
 * @return          encrypted text
 */
function AESEncryptCtr($plaintext, $password, $nBits) {
  $blockSize = 16;  // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
  if (!($nBits==128 || $nBits==192 || $nBits==256)) return '';  // standard allows 128/192/256 bit keys
  // note PHP (5) gives us plaintext and password in UTF8 encoding!
	
  // use AES itself to encrypt password to get cipher key (using plain password as source for  
  // key expansion) - gives us well encrypted key
  $nBytes = $nBits/8;  // no bytes in key
  $pwBytes = array();
  for ($i=0; $i<$nBytes; $i++) $pwBytes[$i] = ord(substr($password,$i,1)) & 0xff;
  $key = Cipher($pwBytes, KeyExpansion($pwBytes));
  $key = array_merge($key, array_slice($key, 0, $nBytes-16));  // expand key to 16/24/32 bytes long 

  // initialise counter block (NIST SP800-38A §B.2): millisecond time-stamp for nonce in 
  // 1st 8 bytes, block counter in 2nd 8 bytes
  $counterBlock = array();
  $nonce = floor(microtime(true)*1000);   // timestamp: milliseconds since 1-Jan-1970
  $nonceSec = floor($nonce/1000);
  $nonceMs = $nonce%1000;
  // encode nonce with seconds in 1st 4 bytes, and (repeated) ms part filling 2nd 4 bytes
  for ($i=0; $i<4; $i++) $counterBlock[$i] = urs($nonceSec, $i*8) & 0xff; 
  for ($i=0; $i<4; $i++) $counterBlock[$i+4] = $nonceMs & 0xff;
  // and convert it to a string to go on the front of the ciphertext
  $ctrTxt = '';
  for ($i=0; $i<8; $i++) $ctrTxt .= chr($counterBlock[$i]);

  // generate key schedule - an expansion of the key into distinct Key Rounds for each round
  $keySchedule = KeyExpansion($key);
  
  $blockCount = ceil(strlen($plaintext)/$blockSize);
  $ciphertxt = array();  // ciphertext as array of strings
  
  for ($b=0; $b<$blockCount; $b++) {
    // set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
    // done in two stages for 32-bit ops: using two words allows us to go past 2^32 blocks (68GB)
    for ($c=0; $c<4; $c++) $counterBlock[15-$c] = urs($b, $c*8) & 0xff;
    for ($c=0; $c<4; $c++) $counterBlock[15-$c-4] = urs($b/0x100000000, $c*8);

    $cipherCntr = Cipher($counterBlock, $keySchedule);  // -- encrypt counter block --

    // block size is reduced on final block
    $blockLength = $b<$blockCount-1 ? $blockSize : (strlen($plaintext)-1)%$blockSize+1;
    $cipherByte = array();
    
    for ($i=0; $i<$blockLength; $i++) {  // -- xor plaintext with ciphered counter byte-by-byte --
      $cipherByte[$i] = $cipherCntr[$i] ^ ord(substr($plaintext, $b*$blockSize+$i, 1));
      $cipherByte[$i] = chr($cipherByte[$i]);
    }
    $ciphertxt[$b] = implode('', $cipherByte);  // escape troublesome characters in ciphertext
  }

  // implode is more efficient than repeated string concatenation
  $ciphertext = $ctrTxt . implode('', $ciphertxt);
  $ciphertext = base64_encode($ciphertext);
  return $ciphertext;
}


/** 
 * Decrypt a text encrypted by AES in counter mode of operation
 *
 * @param ciphertext source text to be decrypted
 * @param password   the password to use to generate a key
 * @param nBits      number of bits to be used in the key (128, 192, or 256)
 * @return           decrypted text
 */
function AESDecryptCtr($ciphertext, $password, $nBits) {
  $blockSize = 16;  // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
  if (!($nBits==128 || $nBits==192 || $nBits==256)) return '';  // standard allows 128/192/256 bit keys
  $ciphertext = base64_decode($ciphertext);

  // use AES to encrypt password (mirroring encrypt routine)
  $nBytes = $nBits/8;  // no bytes in key
  $pwBytes = array();
  for ($i=0; $i<$nBytes; $i++) $pwBytes[$i] = ord(substr($password,$i,1)) & 0xff;
  $key = Cipher($pwBytes, KeyExpansion($pwBytes));
  $key = array_merge($key, array_slice($key, 0, $nBytes-16));  // expand key to 16/24/32 bytes long
  
  // recover nonce from 1st element of ciphertext
  $counterBlock = array();
  $ctrTxt = substr($ciphertext, 0, 8);
  for ($i=0; $i<8; $i++) $counterBlock[$i] = ord(substr($ctrTxt,$i,1));
  
  // generate key schedule
  $keySchedule = KeyExpansion($key);

  // separate ciphertext into blocks (skipping past initial 8 bytes)
  $nBlocks = ceil((strlen($ciphertext)-8) / $blockSize);
  $ct = array();
  for ($b=0; $b<$nBlocks; $b++) $ct[$b] = substr($ciphertext, 8+$b*$blockSize, 16);
  $ciphertext = $ct;  // ciphertext is now array of block-length strings

  // plaintext will get generated block-by-block into array of block-length strings
  $plaintxt = array();
  
  for ($b=0; $b<$nBlocks; $b++) {
    // set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
    for ($c=0; $c<4; $c++) $counterBlock[15-$c] = urs($b, $c*8) & 0xff;
    for ($c=0; $c<4; $c++) $counterBlock[15-$c-4] = urs(($b+1)/0x100000000-1, $c*8) & 0xff;

    $cipherCntr = Cipher($counterBlock, $keySchedule);  // encrypt counter block

    $plaintxtByte = array();
    for ($i=0; $i<strlen($ciphertext[$b]); $i++) {
      // -- xor plaintext with ciphered counter byte-by-byte --
      $plaintxtByte[$i] = $cipherCntr[$i] ^ ord(substr($ciphertext[$b],$i,1));
      $plaintxtByte[$i] = chr($plaintxtByte[$i]);
	  
    }
    $plaintxt[$b] = implode('', $plaintxtByte); 
  }

  // join array of blocks into single plaintext string
  $plaintext = implode('',$plaintxt);
  
  return $plaintext;
}


/*
 * Unsigned right shift function, since PHP has neither >>> operator nor unsigned ints
 *
 * @param a  number to be shifted (32-bit integer)
 * @param b  number of bits to shift a to the right (0..31)
 * @return   a right-shifted and zero-filled by b bits
 */
function urs($a, $b) {
  $a &= 0xffffffff; $b &= 0x1f;  // (bounds check)
  if ($a&0x80000000 && $b>0) {   // if left-most bit set
    $a = ($a>>1) & 0x7fffffff;   //   right-shift one bit & clear left-most bit
    $a = $a >> ($b-1);           //   remaining right-shifts
  } else {                       // otherwise
    $a = ($a>>$b);               //   use normal right-shift
  } 
  return $a; 
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
?>
